1. Field of the Invention
This invention relates to a photographic silver halide material comprising a redox release compound that is capable, upon oxidation, of releasing a silver ion complexing heterocyclic thio moiety which enables reduction of the concentration of silver required in the photographic material. It also relates to such redox release compounds which preferably comprise a silver ion complexing 1,2,4-triazolium-3-thio moiety.
2. Description of the State of the Art
Photographic silver halide materials comprising combinations of surface sensitive photographic silver halide and fogged internally sensitive photographic silver halide are known in the photographic art. Examples of such photographic silver halide materials are described in, for instance, U.S. Pat. No. 4,335,199; U.S. Pat. No. 2,996,382 and U.S. Pat. No. 3,178,282. A problem encountered in such materials has been the need to provide a significant concentration of iodide, such as that released from silver iodide to enable development of the fogged internally sensitive photographic silver halide in such materials. A problem encountered in the photographic materials of U.S. Pat. No. 4,335,199 has been that the photosensitivity of the internally sensitive photographic silver halide must be equal to or greater than the photosensitivity of the surface sensitive photographic silver halide. This is difficult because this requires more total silver in the photographic silver halide material than otherwise might be required. It has been desirable to avoid the need for iodide, such as from silver iodide, and to enable a photographic silver halide material that reduces the concentration of total silver needed to provide a developed image in such photographic materials comprising mixed surface sensitive photographic silver halide and internally sensitive photographic silver halide. It has also been desirable to enable contrast enhancement in such photographic silver halide materials.
A need has also existed for new organic compounds that enable reduction of total silver concentration in a photographic silver halide material comprising a combination of a surface sensitive photographic silver halide and an internally sensitive photographic silver halide.